It's not complicated. The bullet is .001" larger then the bore to allow the bullet to make contact with the rifling as well as seal the barrel. The rifling is the smallest part of the bore, the lands are actually slightly larger. I'm not sure by how much, it may vary from gun to gun but I'm sure someone here knows. If the bullet was the same size exactly it would have very little contact with the rifling and this would cause stability issues. Also, pressure could pass around the bullet causing a severe loss in velocity.

If I see ".22 cal (.224) is that the correct bullet for reloading .223?

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That is actually a good question, gus. There are out there boxes of .223 bullets-used for older .22 Hornet rifles. They would NOT shoot well in your AR. They would not hurt your gun, but the groups would look like #4 BuckShot loads! HA.. I think you said that you have a 1-7" twist==65 to 75 gr. BT bullets should shoot well.

Naming cartridges is a crazy business. Normally they are named by the bore diameter, but you can go by the diameter across the lands or across the grooves. A .223 is normally .223 across the lands but .224 across the groves. A .222 and .222 Mag are the same as the .223. A .270 is actually .277 across the lands. A .38 Special is .358 across the lands as is a .357 Mag (groove diameter). A .480 Ruger is .475. A .44 mag is .429 but a .41 mag is .410 and a 40 S&W is a true 40 caliber using .401 bullets (for a proper seal).

Some of this is historical. The .38 Special was developed from the .38 Long Colt which was developed from the .38 Short Colt which was developed for converted cap and ball .36 caliber revolvers whch had a bore diameter of .38.
.38 sounds bigger than .36 so it is more powerful and marketable. Originally the .38 Short Colt had a heeled bullet like the .22 Long Rifle and was 38 caliber. When the design was updated/improved so the bullet sat inside the case, the bullet had to shrink and the barrels were made in an appropriate diameter for this new bullet (.357-.358). So the 38 special started off life as a true 38 but evolved into a .357 special.

The numerical name tends to carry forward when a cartridge is modernized. What really causes confusion is when some maker decides to be honest and call something by a realistic name like the .357 Magnum. It is difficult for people to grasp that a "huge" .38 caliber bullet can be safely fired through a tiny .357 barrel.

It can get even more confusing when you consider the older black powder cartridges. .25-20 was a .25 caliber bullet propelled by 20 grains of black powder. .32-20 was a .312 diameter bullet propelled by 20 grains of black powder. The .44-40 was a .427 bullet and 40 grains of powder, but the 38-40 was a 40 caliber bullet and 38 grains of powder (bass ackwards naming). I guess 40-38 did not sound right. The 45-70 was actually called the 45-70-500, diamter-powder charge-bullet weight in grains. The 30-30 was never loaded with black powder as it was developed as one of the first smokeless powder cartridges in the US but people were used to that kind of name so it stuck. On a side note, the 30-30 is also known as the 30WCF or Winchester Center Fire. The 30-40 Krag also was developed as a smokeless powder cartridge and was never loaded with black powder. It is also known as the .30 US Government.

Then you get to the .30-06. It was a 30 caliber (.308 diameter) rifle cartridge adopted in 1906. It is an improvement of an earlier cartridge called the .30-03.

The Europeans use a very different method of naming cartridges that in some respects is more clear, once you understand their thought process. The 9mm Luger or Parabellum (for war) is also called the 9 X 19 or 9mm diameter with a 19mm case length. The .380 ACP is known as the 9 X 17. The 7mm Mauser is the 7 X 57 and the 8mm Mauser is the 8 X 57 or sometimes the 7.92 X 57 (don't get me started on the whole .318/.323 diameter, J JS issue). The popularity of break open multi barrel rifles and shotgun/rifle combination guns in Europe causes the need for a rimmed cartridge for these actions. So the Europeans add the letter "R" after the cartridge name to indicate it is rimmed hence the designations 7 X 57R, 8 X 57R, 7.62 X 54R etc.

Now that I have muddied up the waters, you will realize there is much to learn. That is part of the fun of our sport. There is always more to learn.

Robo, correct me if I'm wrong but didn't the 30-30 start out as 30WCF and when Marlin built a rifle of the same caliber they didn't want to put Winchester's name on their rifles so they called it a 30-30 and over time the two names became interchangable.

Naming cartridges is a crazy business. Normally they are named by the bore diameter, but you can go by the diameter across the lands or across the grooves. A .223 is normally .223 across the lands but .224 across the groves. A .222 and .222 Mag are the same as the .223. A .270 is actually .277 across the lands. A .38 Special is .358 across the lands as is a .357 Mag (groove diameter). A .480 Ruger is .475. A .44 mag is .429 but a .41 mag is .410 and a 40 S&W is a true 40 caliber using .401 bullets (for a proper seal).

Some of this is historical. The .38 Special was developed from the .38 Long Colt which was developed from the .38 Short Colt which was developed for converted cap and ball .36 caliber revolvers whch had a bore diameter of .38.
.38 sounds bigger than .36 so it is more powerful and marketable. Originally the .38 Short Colt had a heeled bullet like the .22 Long Rifle and was 38 caliber. When the design was updated/improved so the bullet sat inside the case, the bullet had to shrink and the barrels were made in an appropriate diameter for this new bullet (.357-.358). So the 38 special started off life as a true 38 but evolved into a .357 special.

The numerical name tends to carry forward when a cartridge is modernized. What really causes confusion is when some maker decides to be honest and call something by a realistic name like the .357 Magnum. It is difficult for people to grasp that a "huge" .38 caliber bullet can be safely fired through a tiny .357 barrel.

It can get even more confusing when you consider the older black powder cartridges. .25-20 was a .25 caliber bullet propelled by 20 grains of black powder. .32-20 was a .312 diameter bullet propelled by 20 grains of black powder. The .44-40 was a .427 bullet and 40 grains of powder, but the 38-40 was a 40 caliber bullet and 38 grains of powder (bass ackwards naming). I guess 40-38 did not sound right. The 45-70 was actually called the 45-70-500, diamter-powder charge-bullet weight in grains. The 30-30 was never loaded with black powder as it was developed as one of the first smokeless powder cartridges in the US but people were used to that kind of name so it stuck. On a side note, the 30-30 is also known as the 30WCF or Winchester Center Fire. The 30-40 Krag also was developed as a smokeless powder cartridge and was never loaded with black powder. It is also known as the .30 US Government.

Then you get to the .30-06. It was a 30 caliber (.308 diameter) rifle cartridge adopted in 1906. It is an improvement of an earlier cartridge called the .30-03.

The Europeans use a very different method of naming cartridges that in some respects is more clear, once you understand their thought process. The 9mm Luger or Parabellum (for war) is also called the 9 X 19 or 9mm diameter with a 19mm case length. The .380 ACP is known as the 9 X 17. The 7mm Mauser is the 7 X 57 and the 8mm Mauser is the 8 X 57 or sometimes the 7.92 X 57 (don't get me started on the whole .318/.323 diameter, J JS issue). The popularity of break open multi barrel rifles and shotgun/rifle combination guns in Europe causes the need for a rimmed cartridge for these actions. So the Europeans add the letter "R" after the cartridge name to indicate it is rimmed hence the designations 7 X 57R, 8 X 57R, 7.62 X 54R etc.

Now that I have muddied up the waters, you will realize there is much to learn. That is part of the fun of our sport. There is always more to learn.

Robo, correct me if I'm wrong but didn't the 30-30 start out as 30WCF and when Marlin built a rifle of the same caliber they didn't want to put Winchester's name on their rifles so they called it a 30-30 and over time the two names became interchangable.

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I believe that is indeed correct. Winchester used proprietary names on their cartridges. Others would not give free advertising to Winchester (perhaps there was some copyright issues also) so they would rename the cartridge for their purposes.

You still see this in cartridges like the .38 S&W Special and .44 S&W Special (the actual names) have been used so extensively with out the S&W part of their names many folks forget the real name.

The venerable .44 Remington Magnum has become simply the .44 mag. Remington ammo is still head stamped 44 Rem Mag, but everyone else drops the "Rem" from the name.

Partnerships in new cartridge/gun design have linked arms and ammo makers in several endeavors. When a gun maker is also an ammo maker, it leads to names that others would rather not advertise. S&W, Remington and Winchester each make (or used to make) both guns and ammo. S&W sold there ammo line to Federal, Winchester is pretty much out of the gun business and Remington still makes both but are no longer in the handgun business.

Naming cartridges is a crazy business. Normally they are named by the bore diameter, but you can go by the diameter across the lands or across the grooves. A .223 is normally .223 across the lands but .224 across the groves. A .222 and .222 Mag are the same as the .223. A .270 is actually .277 across the lands. A .38 Special is .358 across the lands as is a .357 Mag (groove diameter). A .480 Ruger is .475. A .44 mag is .429 but a .41 mag is .410 and a 40 S&W is a true 40 caliber using .401 bullets (for a proper seal).

Some of this is historical. The .38 Special was developed from the .38 Long Colt which was developed from the .38 Short Colt which was developed for converted cap and ball .36 caliber revolvers whch had a bore diameter of .38.
.38 sounds bigger than .36 so it is more powerful and marketable. Originally the .38 Short Colt had a heeled bullet like the .22 Long Rifle and was 38 caliber. When the design was updated/improved so the bullet sat inside the case, the bullet had to shrink and the barrels were made in an appropriate diameter for this new bullet (.357-.358). So the 38 special started off life as a true 38 but evolved into a .357 special.

The numerical name tends to carry forward when a cartridge is modernized. What really causes confusion is when some maker decides to be honest and call something by a realistic name like the .357 Magnum. It is difficult for people to grasp that a "huge" .38 caliber bullet can be safely fired through a tiny .357 barrel.

It can get even more confusing when you consider the older black powder cartridges. .25-20 was a .25 caliber bullet propelled by 20 grains of black powder. .32-20 was a .312 diameter bullet propelled by 20 grains of black powder. The .44-40 was a .427 bullet and 40 grains of powder, but the 38-40 was a 40 caliber bullet and 38 grains of powder (bass ackwards naming). I guess 40-38 did not sound right. The 45-70 was actually called the 45-70-500, diamter-powder charge-bullet weight in grains. The 30-30 was never loaded with black powder as it was developed as one of the first smokeless powder cartridges in the US but people were used to that kind of name so it stuck. On a side note, the 30-30 is also known as the 30WCF or Winchester Center Fire. The 30-40 Krag also was developed as a smokeless powder cartridge and was never loaded with black powder. It is also known as the .30 US Government.

Then you get to the .30-06. It was a 30 caliber (.308 diameter) rifle cartridge adopted in 1906. It is an improvement of an earlier cartridge called the .30-03.

The Europeans use a very different method of naming cartridges that in some respects is more clear, once you understand their thought process. The 9mm Luger or Parabellum (for war) is also called the 9 X 19 or 9mm diameter with a 19mm case length. The .380 ACP is known as the 9 X 17. The 7mm Mauser is the 7 X 57 and the 8mm Mauser is the 8 X 57 or sometimes the 7.92 X 57 (don't get me started on the whole .318/.323 diameter, J JS issue). The popularity of break open multi barrel rifles and shotgun/rifle combination guns in Europe causes the need for a rimmed cartridge for these actions. So the Europeans add the letter "R" after the cartridge name to indicate it is rimmed hence the designations 7 X 57R, 8 X 57R, 7.62 X 54R etc.

Now that I have muddied up the waters, you will realize there is much to learn. That is part of the fun of our sport. There is always more to learn.